The present invention is directed to an improved temperature probe based on contact technology for low pressure processing of semiconductors, and to an improved method of measuring temperature in such processes.
The manufacture of semiconductor devices such as integrated circuits from semiconductor wafers may involve a number of steps. It may be necessary to carry out some of these steps in a low pressure environment where the pressure may be less than about 10 torr. Since the normal atmospheric pressure in the air at sea level is 760 torr, it can be seen that the processing may take place at only a small fraction of atmospheric pressure.
In the performance of many such processes, it is necessary to monitor the temperature of the semiconductor wafer. This is usually done with the use of a temperature probe which contains a temperature sensor such as a thermocouple, in contact to the wafer. It has been found that when a temperature probe is used in a low pressure process as described above, the reading provided by the temperature sensor does not closely follow the actual temperature of the wafer. This causes a problem because accurate temperature readings are necessary to monitor and control the production process.
The present inventors believe that the problem is caused by the fact that at low pressure, the thermal conductivity of gases in the reaction chamber becomes low. That is, while the wafer and the temperature probe appear to the naked eye to be contacting each other, at a microscopic level, the contact is sporadic rather than continuous, and the space between contact points is at a pressure which is the same as or close to the low pressure at which the process is performed. Since at such low pressure, the thermal conductivity of gases is low, the rate of heat transfer between the wafer and the contact surface of the probe is not good enough for the temperature sensor to rapidly respond to changes in the actual temperature of the wafer.
U.S. Pat. No. 5,791,782, the contents of which are in their entirety incorporated by reference, discloses a temperature probe wherein the probe freely pivots on the support under the weight of the semiconductor wafer so as to maintain close contact therewith. This suitably improves the responsiveness of the temperature sensor in a higher pressure environment. Although one of the objects of the prior patent is to provide temperature measurements which closely follow the actual temperature of the wafer in a vacuum or low pressure environment, the inventors herein have ascertained that the configuration of the prior patent does not accomplish this.